Mechanism Study On Mercury Removal By Cu-based Sorbents

Atmospheric mercury pollution is of global concern due to its volatility,strong neurotoxicity and bioaccumulation. Fossil fuel combustion is one of thebiggest anthropogenic mercury emission sources in the world. Consequently, themercury emission limits for coal-fired power plants are more and more stringent.Using existing air pollution control devices may not be able to reach the strictenvironmental limitations. It is necessary to apply the sorbent injectiontechnology to control mercury emission. The research of mercury sorbents withhigh efficiencies and low costs are of great significance for mercury removal incoal-fired power plants.Copper chloride (CuCl2) and copper oxide (CuOx) had been chosen as activematerials, and neutral alumina, artificial zeolite and activated carbon had beenselected as the carriers in this study. Cu-based sorbents were prepared by wetimpregnation method and the mercury removal efficiencies were tested infixed-bed reactor system. The mercury oxidation rates and adsorption rates weretested under different simulated flue gas components and the temperature rangewas60-300°C. The BET, XRD and TEM methods were employed to analyze thespecific area, total pore volume, crystal species and microstructures of themodified sorbents. The XPS and TPR methods were used to analyze the coppervalence. The catalytic oxidation mechanisms for modified non-carbon sorbentswere proposed based on analytical results.The results indicate that the mercury removal capacities of the carriers hadbeen significantly improved after impregnation. HCl could promote the mercuryremoval process, while SO2, NO and water vapor had a negative effect. Theinhibition of SO2and water vapor were stronger than that of NO. CuCl2impregnated activated carbon and CuOximpregnated neutral alumina had strongsulfur resistance in the presence of HCl. Higher temperature restrained theadsorption of mercury and improve mercury catalytic oxidation. The catalyticoxidation mechanism of CuCl2impregnated neutral alumina could be explainedby the Eley-Rideal mechanism. The mercury catalytic oxidation reaction of CuOximpregnated neutral alumina followed the Mars-Maessen mechanism.CuCl2impregnated neutral alumina and CuCl2impregnated artificial zeolitehad similar initial adsorption rates with modified activated carbon. As thecontact time of sorbents and flue gas was very short in coal-fired power plants,CuCl2impregnated non-carbon sorbents might be good alternatives to activatedcarbon for reducing the mercury removal cost. CuOximpregnated neutralalumina was a good multi-function sorbent with high initial adsorptionefficiency and high mercury oxidation rate. It could be an alternative toactivated carbon.Sorbent injection of CuCl2impregnated neutral alumina and CuCl2impregnated artificial zeolite had been tested in a coal-fired power plant inChina. The results showed that the modified sorbents could effectively reducemercury with good mercury removal capacity. Compared to activated carbonsorbents, the costs of non-carbon sorbents were lower and the applications ofnon-carbon sorbents might have great potential in China.